The invention relates to a multiple filter, the use of such a multiple filter as a plug connector and to a method for producing such a multiple filter.
Multiple filters are known per se. In many cases, planar filters are used in which the capacitor electrodes are provided in a plane at right angles to the alignment of the signal conductors. As a consequence, only limited capacitances can be accommodated in the limited space on the bases of such planar filters. For larger capacitances, filters have been developed which surround the signal conductors like tubular capacitors. This makes larger electrode areas possible and larger capacitances can be achieved, which can be further increased by the use of dielectrics with dielectric constants of the order of magnitude of 103 to 104, for example as disclosed in U.S. Pat. No. 4,494 092, in French Patent Document FR 2 422 268 or in Published, Non-Prosecuted German Patent Applications DE-OS 26 00 320 or DE-OS 28 00 745.
It is accordingly an object of the invention to provide a multiple filter, in particular for plug connectors, which overcomes disadvantages of the heretofore-known multiple filters of this general type and which can be produced easily and economically. A preferred embodiment of the multiple filter should be usable in the frequency range of up to and above 10 GHz. The multiple filter should have the capability of not only being fitted with discrete components but also with thick or thin-film technology. The multiple filter should furthermore operate in a reliable and safe manner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a first embodiment of a multiple filter, including:
a cuboid block made of an insulating material and having an exterior region;
the cuboid block being formed with a number of passages to be assigned to a corresponding number of signal conductors;
at least one capacitor being respectively assigned to each of at least some of the passages;
the at least one capacitor having a signal electrode and a ground electrode and a dielectric layer provided therebetween;
the signal electrode being electrically connected to an associated one of the signal conductors;
a ground conductor connectable to ground;
the dielectric layer including a dielectric with a dielectric constant in an order of magnitude of 103 to 104, the dielectric being formed of the insulating material;
the at least one capacitor being in a form of a capacitor column;
the capacitor column being provided in the cuboid block and being surrounded by the cuboid block, the capacitor column being formed with a central channel and having an outer wall, the central channel forming one of the passages;
the signal electrode of the at least one capacitor being formed in the central channel; and
the ground electrode being provided in a region of the outer wall of the capacitor column, the ground electrode being a metal layer at least partially covering the outer wall and
being connected to the ground conductor extending transversely to the central channel.
A second embodiment of the multiple filter includes:
a cuboid block made of an insulating material and having a base and an exterior region;
the cuboid block being formed with a number of passages to be assigned to a corresponding number of signal conductors;
capacitors being respectively assigned to each of at least some of the passages;
the capacitors each having a signal electrode and a ground electrode and a dielectric layer provided therebetween;
the signal electrode being electrically connected to an associated one of the signal conductors;
a ground conductor connectable to ground;
the dielectric layer including a dielectric with a dielectric constant in an order of magnitude of 103 to 104, the dielectric being formed of the insulating material;
the capacitors being in a form of capacitor columns and having feet;
the capacitor columns standing with the feet on the base of the cuboid block and being separated as islands at least by transverse grooves formed in the cuboid block;
the capacitor columns each being formed with a central channel having an inner wall, and the capacitor columns each having an outer wall, the central channel forming one of the passages;
the signal electrode being provided in a region of the inner wall; and
the ground electrode being provided in a region of the outer wall, the ground electrode being a metal layer at least partially covering the outer wall and being connected to the ground conductor extending transversely to the central channel.
In accordance with another feature of the invention, a metallic coating is connected to the central channel, the metallic coating forming the signal electrode.
In accordance with yet another feature of the invention, the ground electrode is a metallization, the metallization surrounds the capacitor columns in a manner of a tube.
In accordance with a further feature of the invention, the cuboid block is formed with grooves; and shielding metal strips are introduced in at least some of the grooves and are connected to ground.
In accordance with another feature of the invention, the cuboid block is formed with grooves, the grooves have respective bases; and ground conductors are provided in the bases of the grooves.
In accordance with another feature of the invention, an associated one of the signal conductors is provided at a distance from the signal electrode and thus from the dielectric; the signal electrode is subdivided into at least two electrode elements separated in a direction of a signal propagation; and the electrode elements are electrically connected, via at least one signal connecting conductor, with the associated one of the signal conductors such that the at least one capacitor is formed from capacitor elements and includes a continuous electrode and a subdivided electrode.
In accordance with yet another feature of the invention, the at least one signal connecting conductor and the associated one of the signal conductors are connected by an essentially point-shaped connection; and a further dielectric having a further dielectric constant in a range from 100 to 101 is provided between the associated one of the signal conductors and the signal electrode.
In accordance with a further feature of the invention, the ground conductor is provided at a distance from the ground electrode and thus from the dielectric; the ground electrode is subdivided into at least two electrode elements separated in a direction of a signal propagation; and the electrode elements are electrically connected, via at least one ground connecting conductor, with the ground conductor such that the at least one capacitor is formed from capacitor elements and includes a continuous electrode and a subdivided electrode.
In accordance with a further feature of the invention, the ground connecting conductor and the ground conductor are connected by an essentially point-shaped connection; and a further dielectric having a further dielectric constant in a range from 100 to 101 is provided between the ground conductor and the ground electrode.
In accordance with another feature of the-invention, the ground conductor is a metallized strip running parallel to the central channel, at a distance from the dielectric having a dielectric constant in a range from 103 to 104.
In accordance with yet another feature of the invention, the further dielectric is provided as a spacer between the metallization and the dieletric.
In accordance with another feature of the invention, electronic components connect the subdivided and mutually insulated electrode elements in series.
In accordance with another feature of the invention, the electronic components are resistance elements with resistance values in a range of a characteristic impedance of the associated one of the signal conductors interacting with the dielectric.
In accordance with yet another feature of the invention, the resistance elements are ohmic resistance elements.
In accordance with another feature of the invention, the electronic components are resistance elements with resistance values in a range of a characteristic impedance of the ground conductor interacting with the dielectric.
In accordance with a further feature of the invention, soldered SMD components are provided as resistors for connecting adjacent ones of the electrode elements in series.
In accordance with a further feature of the invention, applied strips of resistance paste connect adjacent ones of the electrode elements in series.
In accordance with yet another feature of the invention, resistance strips are applied with planar technology, the resistance strips connecting adjacent ones of the electrode elements in series.
In accordance with a further feature of the invention, an inductance is connected to the signal conductor and/or the ground conductor.
In accordance with another feature of the invention, the signal electrode and/or the ground electrode is subdivided into electrode elements, an inductance is connected between two successive ones of the electrode elements, the inductance is in a range of from 1 to 10 xcexcH and is selected from the group consisting of SMD coils, ferrite beads, and ferrite layers.
In accordance with a further feature of the invention, at least one of the ground conductor, the dielectric, the further dielectric, the signal conductors, electrode elements, a resistance, and an inductance is a layer applied as a screen-printed layer for forming a planar filter structure.
In accordance with another feature of the invention, a plurality of capacitor columns is provided in a row and grouped as one of single columns, double columns, triple columns, and multiple columns for forming plug connector inserts, the capacitor columns having respective central channels for the associated signal conductors to pass therethrough, a base for the capacitor columns corresponding to connections to be filtered, and the ground conductor being a metallic coating provided on at least part of outer walls of the capacitor columns.
The multiple filter may advantageously be used in combination with a multipole plug connector.
With the objects of the invention in view there is also provided a method for producing a multiple filter according to the invention, the method includes the steps of:
providing a cuboid block made of an insulating material;
providing capacitors having a dielectric with a dielectric constant in an order of magnitude of 103 to 104, the capacitors being in a form of capacitor columns and having central channels;
applying signal electrode elements and/or ground electrode elements by applying and burning a metallization paste in strips on outer surfaces of the capacitor columns;
applying a layer of a further dielectric having a further dielectric constant in a range from 100 to 101 over the signal electrode elements and/or the ground electrode elements; and
providing the layer of the further dielectric with centrally located apertures and passing connecting conductors therethrough for connecting the signal electrode elements to a signal conductor and the ground electrode elements to a ground conductor.
In accordance with another mode of the invention, a screen-printing process is used for the steps of applying the metallization paste and/or applying the further dielectric.
In accordance with another mode of the invention, the layer of the further dielectric is provided with further apertures in a region of at least two successive electrode elements; and resistance strips are applied on the layer of the further dielectric for connecting the further apertures.
In accordance with another mode of the invention, ground conductor strips and/or resistance strips are applied as on-edge metal strips; a solder paste is introduced into the apertures and a subsequent soldering is performed for producing an electrical connection to respective ones of the ground electrode elements and the signal electrode elements, wherein the electrical connection passes through the apertures.
In accordance with another mode of the invention, the signal conductor and/or the ground conductor are provided with ferritic coverings between connecting points of the connecting conductors.
In accordance with another mode of the invention, a ferritic paste is applied to the signal conductor and/or the ground conductor by using a screen-printing process.
In plug connectors, the contacts to be connected (in the following text referred to as signal conductors) are provided in rows. A multiple filter which can be installed in the plug connector must therefore have a configuration corresponding to this contact pattern. One embodiment of the multiple filter according to the invention is formed by capacitors provided in rows and columns, which are joined together to form a block; each has a channel for the associated signal conductor to pass through as well as a ground conductor for connection to a ground point, if necessary via bridging conductors which join the ground conductors of the capacitors.
Each of the capacitors is in the form of a capacitor column with a central channel for the associated signal line to pass through, with the dielectric material forming the block which contains the individual capacitors. Metal coatings on the insides of the central channels, which are electrically connected to the signal lines passing through, form signal electrodes of the capacitors, and metal coatings on the outsides of the capacitor columns form the ground electrodes. When high dielectric strength material with a low dielectric constant is used, sufficiently high capacitances can be achieved, which still allow effective filtering, but whose capacitance has a low temperature and frequency response. If, on the other hand, a material with a high dielectric constant is used, individual capacitors with extremely high capacitance values can be achieved. A number of such capacitor columns corresponding to the hole pattern of the plug connector are combined to form a block, so that its plug pattern corresponds to that of a corresponding plug connector. In this case, different capacitor columns can be joined and different conductor connectors may also be used, for example coaxial contacts and/or power-current contacts in addition to signal contacts. For production purposes, the dielectric body is advantageously produced using the injection-molding method or using a method similar to centrifugal casting from an appropriate ceramic slip, in which case fine structures can be produced in particular with the method that is similar to centrifugal casting.
In the first embodiment, the joined capacitor columns form a cuboid block. Each of the capacitor columns is provided with a central channel for the signal conductor to pass through, with the inner wall of the central channel being metallized to form the signal electrode. At a distance from this, this signal electrode is surrounded by a metallized coating which forms the ground electrode, with the dielectric layer being provided between the two to maintain the spacing. The ground electrodes of the individual capacitors are advantageously fed out via one or more bridge electrodes for metallization of the end surface, and are connected to the general ground. The totally metallized end surface or elsexe2x80x94in the case of filters provided in seriesxe2x80x94metallized strips running on the end face form the ground connection (it is self-evident that the areas between the ground electrodes and the signal electrodes are excluded from metallization). This embodiment forms a compact block of assembled capacitors, which can be introduced as such directly into a circuit. Such structures can be produced on the basis of extruded hollow tubes, through whose central channel the signal conductor is passed, and whose outside is metallized. These are joinedxe2x80x94depending on the desired quantity and configurationxe2x80x94to form a block and are then sintered, if required with the interposition of a dielectric having a low dielectric constant. The sintered block is machined to size and is contacted, the individual signal conductors are inserted into the central channels, and either themselves form the signal electrode resting on the dielectric or are connected, in the central channel, to the internal metallized areas in the central channels, which form the coatings of the signal electrode. Capacitance matching can in this case be carried out by cutting the capacitor columns or their metallic outer coatings to length; alternatively, the inner coatings can also be cut to length, although an air gap must then be provided between the dielectric and the signal conductor, to allow this type of capacitance matching. If the signal electrode and/or the ground electrode are offset with respect to the end surface, the dielectric strength can be further increased.
In this first embodiment, the block of the multiple filter can be configured to be so compact that the central channel with the signal conductor and the ground dissipation conductor, which is connected to the equipment ground via the ground conductor, can become conductor tracks which are applied onto dielectric layers. The metallized end faces of the base (or its metallized surface areas) are then available as a ground connection.
In a second embodiment, the individual capacitors are separated from one another like islands through the use of mutually crossing grooves in the dielectric block, so that a column structure is produced which is provided in a trough and in which each of the columns is a capacitor column whose foot is anchored in the block. Significant decoupling between the individual capacitors is in this case achieved just by these air gaps. Each capacitor column contains a central channel for the signal conductor, which forms the signal electrode or which is connected to the inner channel wall which is metallized to form the signal electrode, and an outer coating which is provided on the outside and forms the ground electrode of the associated capacitor, which is connected to the connecting points via a bridge electrode or bridge electrodes provided in the base of the grooves, as already described. In this case, the insides of the side walls of the trough are advantageously metallized, and the bridge electrode passes via this metallization with the ground connecting point or points provided on the outside of the block.
In this second embodiment, the block of the multiple capacitor can also be configured such that wall areas which surround the capacitor columns standing on the base do not extend to the height of the columns, ending flush with them. In fact, the heights of these wall areas can be lower than the capacitor columns, or they may be entirely omitted with the capacitor columns standing freely on the base. The metallized end faces of the base (or its metallized surface areas) are then available as a ground connection.
The capacitance trimming can be achieved either by varying the column height or by trimming the area of the metallized coating of the signal or ground electrode. This area trimming is advantageously achieved by laser removal using a laser trimming apparatus so that, in this configuration as well, the individual capacitances of each of the capacitors can be set to a desired, tightly-toleranced value. All four sides of the columns are advantageously metallized, thus shielding the individual capacitors from one another, completely decoupling them, suppressing undesirable crosstalk and, because of the shielding against electrical fields, improving the pulse immunity to EMP somewhat. A printable palladium-silver suspension is for example used in a manner known per se for metallization, which remains as a metallic coating on the surface during sintering of the green body produced by injection molding or centrifugal casting, and this coating can be soldered in order to produce the electrical connection.
Alternatively, the metallization in particular of the outer coatings is applied after sintering, for example by printing with subsequent heating, through the use of electroplating technology or through the use of metallic coating in a vacuum, through the use of plasma or the like. The capacitor columns are advantageously not metallized on all sides, or the ground electrodes offset from the end face in order to increase the dielectric strength. Metal strips, introduced into the grooves between the columns, allow improved shielding, although the coupling capacitances in this capacitor system are intrinsically low. Crosstalk phenomena or interference signal scatter are suppressed. In order to improve the mechanical robustness, it is advantageous to encapsulate the ceramic block subdivided in this way with a plastic having a low dielectric constant. In consequence, the crossing grooves are filled, and the electrical characteristics remain essentially unchanged owing to the low dielectric constant. Such filter bodies with capacitors associated with at least a number of signal conductors, constructed in particular with dielectrics having a high dielectric constant of more than 103 have operational limits, however, owing to unavoidable delay-time effects, these limits become apparent where such delay-time time effects prevent simultaneous charging of the capacitor. This is due to the fact that, because of the extent of the capacitor electrodes in the direction of signal propagation running directly on a medium of high dielectric constant in the range 103 to 104, the propagation speed of the signal on the conductor is reduced, and the charging and discharging of the capacitors cannot follow the oscillations in this case.
This raises the more far-reaching problem of extending such a delay-time governed limit to higher and very high frequency ranges in order to extend the applicability in terms of frequency range. In order to achieve this, a development of the invention proposes that each of the signal conductors or the ground conductor or conductors run at a distance from the coatings, so that the high dielectric constant of the capacitor dielectric can no longer have any influence on these conductors; relatively small gaps with a low dielectric constant are generally sufficient for this purpose. Signal or ground conductors thus do not run on the dielectric of the capacitors having a high dielectric constant, but in a medium with a dielectric constant in the region of 100. The signal propagation speed corresponds to that in air and may thus be regarded as being xe2x80x9cundelayedxe2x80x9d, for which purpose relatively small gap widths with a low dielectric constant are generally sufficient.
To this end, that signal electrode of the capacitor which is connected to the signal conductor or that ground electrode of the capacitor which is connected to the ground conductor is subdivided into electrode elements which are electrically individually connected to the signal conductor or the ground conductor and are at a distance from the dielectric having a high dielectric constant. Since they are at a distance from the dielectric constant of the order of magnitude of 103 to 104, the signal propagation speed is not reduced, and undisturbed charging and discharging of the capacitors can take place at frequencies of 1 GHz or more. In order to subdivide the signal electrode into electrode elements, it is sufficient if the diameter of the signal conductor is less than the diameter of the central channel and the signal electrodes are configured as rings fitted onto the wall of the central channel and insulated from one another, with each ring being connected to the signal conductor independently of the others. A dielectric with a dielectric constant in the region of 100 is provided to maintain the spacing in the space between the signal conductor and the wall. In order to subdivide the ground electrode, it is fitted in strips onto the outside of the capacitor column; each strip is connected to a ground conductor, which is provided at a distance from the dielectric and the space in between can be filled, in order to maintain the spacing, with a dielectric having a dielectric constant in the region of 100. Since the signals propagate without any disturbance on the signal or ground conductor provided at a distance from the dielectric, the signal voltages are applied (virtually) simultaneously to the connecting conductor associated with a capacitor element; the individual electrode elements are thus charged and discharged (virtually) simultaneously. This xe2x80x9csimultaneityxe2x80x9d suppresses delay-time differences and shifts their disturbing influence area to higher frequencies. Each of the connecting conductors is advantageously connected roughly at a point to the associated signal or ground conductor, to be precise centrally with respect to the associated capacitor element, in which case xe2x80x9ccentrallyxe2x80x9d relates to the center of the electrode element lying in the propagation direction of the signals. This defines the charge state of the conductor which brings about the xe2x80x9cvirtuallyxe2x80x9d simultaneous charging and discharging of the subdivided capacitor.
In order to keep the ground conductor at a distance from the dielectric in the one embodiment, the ground conductor for each of the capacitor columns is laid as a conductive strip parallel to the central channel at a distance from the dielectric, with a dielectric having a dielectric constant in the region of 100 forming the intermediate layer. With this configuration and in the case of hole patterns having two rows, it is advantageous to lay the ground electrodes on the outsides. For three-row and multi-row hole patterns, the mutually facing sides of the capacitor columns in the inner rows are provided with the ground conductor; since, as a rule, the central channels in such configurations have a gap, the ground conductor can also be accommodated as a web standing on edge.
In order to match their electrical characteristics, the mutually insulated electrode elements are connected via electronic components like a series circuit, for example via resistors which are advantageously in the form of SMD components, varistors or the like. Pure, non-reactive resistors are preferably provided as the resistance elements. Since the propagation speed of the signals on the signal or ground conductor depends on the dielectric constant of the material surrounding this conductor, and discontinuities are formed in signal-carrying conductors when resistors are connected, the resistance values of these resistors should be in the region of the characteristic impedance of the signal or ground conductor which is interacting with a dielectric having a high dielectric constant, thus resulting in the connection-dependent discontinuities being kept low. These components are soldered to two adjacent electrode elements, and electrically connect these adjacent electrode elements to one another. Varistors are also suitable for voltage limiting, in particular to achieve peak-voltage limiting for shock loads, in which case the value of the limit voltage can be achieved by selection of the varistor or of the material which acts like a varistor. Alternatively, strips of a resistance paste, preferably applied by screen-printing methods, can be provided, which connect two adjacent conductor areas to one another in the same way and are thus provided in the area between the subdivided coatings.
Apart from purely ohmic (non-reactive) resistors, inductive elements can also be provided for connection of signal or ground conductors, and in consequence also provide an inductive component. To this end, the signal conductor or the ground conductor or ground dissipation conductor is connected to at least one inductance, for which purpose SMD coils may be provided, or else, alternatively, strips, beads or rings composed of a ferritic material on the signal or ground conductor, since their reaction increases the self-induction of the signal conductor or ground conductor in the area of such strips or rings to an extent which depends on the geometry and the material; this increase can thus be matched to the requirements by selection of these parameters. These inductances are advantageously provided between at least some of the connecting points of the connecting conductors of two successive electrode elements in the subdivided signal or ground electrodes. This configuration results in filters having parallel-connected parallel-path capacitors, which are connected via series-path inductances. The filter characteristics of such configurations can be matched to the requirement by selection of the ring material and/or of the capacitors. Furthermore, it is also possible to introduce inductive componentsxe2x80x94for example SMD coilsxe2x80x94in the free-running signal or ground conductor, and these are then connected in series with the signal or ground connection. Such inductances are preferably provided between the connecting points of the connecting conductors of two successive electrode elements of signal or ground electrodes which are subdivided into individual electrode elements. Thus, by interaction with these series-path inductances and by interaction with the parallel-connected parallel-path capacitors, this results in filters whose filter characteristics can be matched to the requirement by selection of the ring material and/or of the capacitors. Furthermore, it is also possible to introduce inductive componentsxe2x80x94for example SMD coilsxe2x80x94in the free-running signal or earth conductor, which are then connected in series with the signal or ground connection.
Such a multiple filter is advantageously provided with external metallization which on the one hand forms a shield against interference signals, and on the other hand is also configured such that it forms the housing of the filter plug, whose interior is formed by the multiple filter. This metallization in this case also forms the mating contact for the ground connection supplied (or to be dissipated) via a connecting plug.
In order to produce such a filter with subdivided ground electrodes, these are applied in strips onto the dielectric, and this can be done, for example, using the screen-printing method. A further layer composed of a dielectric having a low dielectric constant is applied over the ground electrode, but this has holes in the middle. The ground conductor is now applied to this dielectric layer, at a distance from the dielectric having a high dielectric constant, for passing through the holes, and is conductively connected to the ground electrodes.
This ground conductor is advantageously applied as longitudinally running strips parallel to the axis, for example once again through the use of the screen-printing method; if larger cross sections are required, these strips may also be in the form of conductors standing on edge. This configuration results in the side areas of the electrode elements remaining free and being available for electrical components between the electrode elements. In this configuration, the electrode elements follow one another in the propagation direction of the signal. Although the propagation of the charge on them is delayed owing to the direct contact with a dielectric having a high dielectric constant, the individual electrode elements of each capacitor are charged and discharged (virtually) simultaneously, since the ground conductor (or the signal conductor with the, appropriate configuration) is located in a region with a low dielectric constant, and the signal propagation speed thus (virtually) corresponds to the signal propagation speed in a vacuum.
Since the electrode elements are connected virtually at a point to the ground conductor, delay-time differences may at most arise in charge propagation on the electrode elements, but not in the area of the capacitor overall.
These resistors which match the electrical characteristics are produced as resistance paste applied in strips and are advantageously provided close to the edge, and thus symmetrically about the central ground conductor. They are applied to an insulating layer which is applied, for example using the screen-printing method, to the metallized areas of the capacitor elements connected to the ground conductor. The insulating layer contains a cutout for each of the electrode elements, via which contact is made with the resistance strips, whose resistance values should in this case be in the region of the characteristic impedance of the signal or ground conductor which is interacting with the dielectric having a high dielectric constant. This configuration results in connection-dependent discontinuities being kept small. Other components may also be provided, for example layers with a varistor-like behavior. The inductances which increase the inductance of the ground conductor are applied in layers, as ferritic materials, between the connecting holes to the electrode elements: this application process is also advantageously carried out using the screen-printing method. These ferritic layers increase the series-path inductances of the ground conductor section; together with the two associated capacitor elements as parallel-path capacitors, each of these sections then form Pi filters, whose parameters are established via the capacitor capacitances and the magnitude of the series-path inductances between them. It is self-evident that the meaning of what has been said with regard to the ground conductor also applies to the signal conductor, which is then connected to signal electrodes which have been subdivided into electrode elements, separated from the dielectric having a high dielectric constant. It is also self-evident that structures as have been described here with reference to thick-film technology can also be produced by photolithographic methods and application of corresponding layers in the manner known from production of thin-film technology components.
Due to their block-like structure, such multiple filters can be introduced directly into plug connectors, so that multipole filter plug connectors are available which can be used up to high frequency ranges, can be produced economically and are reliable in operation. If these multiple filters are matched to the dimensions of mating plug connectors, and are provided with external ground connectionsxe2x80x94for example by external metallizationxe2x80x94they may themselves be used as filter plugs.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a multiple filter, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.